Solar control pigmented thermoplastic polymer sheet

ABSTRACT

A solar control light transmitting thermoplastic polymer sheet is provided which contains flakes of metal pigment that are aligned coplanar with the upper face of the sheet. The sheet transmits a controlled amount of light while reflecting a significant amount and absorbing the rest. In an alternative, the sheet has a co-extruded second layer of UV-protective thermoplastic polymer formed on top of the first layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from PCT International Application No.PCT/IL99/00144, filed Mar. 15, 1999, entitled “A SOLAR CONTROL PIGMENTEDTHERMOPLASTIC POLYMER SHEET” which in turn claims benefit from U.S.Provisional Application Ser. No. 60/096,531, filed Aug. 13, 1998 andentitled “A SOLAR CONTROL POLYCARBONATE SHEET”.

FIELD OF THE INVENTION

The present invention relates to outdoor building materials, in general,and to solar control thermoplastic polymer sheets for roofing andcladding, in particular.

BACKGROUND OF THE INVENTION

In the industrial and residential building sectors there is an existingmarket for light-transmitting sheet materials that allow natural lightto enter the building or covered space One of the requirements forlight-transmitting sheets for building is a service temperature of up to80-90° C. and down to −30° C. Furthermore, the sheet should be UVresistant for 20-50 years in extreme radiation conditions, an issuewhich is made more important by the ozone hole problem. The lighttransmission (LT %) should be controllable, with typical values of15-50%. The sheet should have a low Total Solar Transmission (ST_(t)),which is the percent of incident solar radiation transmitted by thesheet, including both the solar transmission and the part of the solarabsorption reradiated inward. As well, the sheet should have a lowShading Coefficient (SC), which is a measure of the total solartransmission relative to that of standard glass. Preferably, the ratioof LT % to ST_(t) of the sheet is high, signifying maximum lighttransmission with minimum heat. Finally, the sheet should be resistantto corrosion and environmentally friendly.

Existing light-transmitting sheets are shown in FIGS. 1A, 1B, 1C and 1D,to which reference is now made. FIG. 1A is a schematic illustration of across-section of a prior art sheet 10 which is clear and not tinted. Thesheet 10 is composed of clear, untinted material 12 such aspolycarbonate (PC), polyvinylchloride (PVC) or fiberglass. The sheet 10allows most of the incident ultraviolet (UV), visible and near infrared(NIR) radiation, shown as solid lines, to pass through it unabsorbed.However the transmitted solar radiation, shown as dashed lines, thenheats the covered space under the sheet 10, which causes thermal stresson people and increases the work to be done by air conditioning systems.

FIG. 1B is a schematic illustration of a cross-section of a prior art,sheet 14 which is clear and tinted, the sheet material comprising aclear polymer 16 with an absorbing pigment 18. Examples of the sheetmaterial are tinted glass and tinted PC. Some of the incident radiation,shown by solid lines, is absorbed by the pigment 18 and some istransmitted. The transmitted radiation, shown by dashed lines, heats thecovered space. The absorption, shown by squiggles, causes thetemperature of the sheet itself to rise. The heated sheet subsequentlyremits the energy at far infrared (FIR) wavelengths, as shown by thecurvy lines. The portion of the reemitted FIR radiation transmittedinward contributes to further heating of the covered space.

FIG. 1C is a schematic illustration of a cross-section of a prior artglass sheet 20, coated with a reflective coating 22 that reflects partof the incident radiation, shown by solid lines, rather than absorbingit. A protective layer 24 coats the reflective coating 22, and protectsit from corrosion. However, the reflective coating 22 is stillsusceptible to corrosion on the edges of the sheet 20 and on the surfacein the event that some of the protective layer 24 has been removed,scratched or dented. Reflective glass is brittle and is unavailable as acorrugated roofing material.

FIG. 1D is a schematic illustration of a cross-section of a prior artplastic sheet 20′, coated with a metallic coating 22′ that reflects partof the incident radiation, shown by solid lines, rather than absorbingit. A protective layer 24′ coats the metallic coating 22′, and protectsit from corrosion. However, the metallic coating 22′ is stillsusceptible to corrosion on the edges of the sheet 20′ and on thesurface in the event that some of the protective layer 24′ has beenremoved, scratched or dented. The metallic coating 22′ can be applied toflat lo sheets only and cannot be applied to corrugated sheets.

German Patent DE19520062 to Moench describes a method of manufacturing aplastic sheet using metal particles, the resulting sheet reflecting IRrays but allowing visible light and UV rays to pass through it. Moenchdescribes aluminum or bronze as the ideal choice for the metalparticles. There are several problems with sheets according to Moench.First of all, it is well known in the art that aluminum reflects IR,visible and UV light in the same proportion. Therefore, it is notpossible that a plastic sheet containing particles of aluminum willselectively reflect IR light and let visible and UV light to passthrough it. Bronze will reflect slightly more IR light than it reflectsvisible and UV light, but the difference from aluminum is notsignificant. Secondly, the purpose of the sheet is as a transparentbuilding material that controls how much the building is heated by lightHowever, it is well known that all light entering a building, IR,visible and UV will contribute to the heat inside the building.Therefore, a sheet according to Moench which is permeable to visible andUV light will still contribute to the heat inside the building. Thirdly,the metal particles according to Moench are spherical, which have lowreflectance efficiency.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide alight-transmitting, thermoplastic polymer sheet material that can beused as an outdoor building material and which overcomes the limitationsand disadvantages of existing materials.

There is provided in accordance with a preferred embodiment of thepresent invention a rigid light transmitting thermoplastic polymer sheethaving an upper face. The sheet includes transparent thermoplasticpolymer having flakes of metal pigment dispersed therein. The flakes areoriented coplanar to the upper face.

There is also provided in accordance with another preferred embodimentof the present invention a rigid light transmitting thermoplasticpolymer sheet including a first transparent thermoplastic polymer layerand a second UV-protective transparent thermoplastic polymer layerco-extruded with the first layer. The second layer is formed on top ofthe first layer. The sheet also includes metal pigment dispersed withinat least one of the first and second layers.

In accordance with a preferred embodiment of the present invention, themetal pigment is dispersed within the first transparent thermoplasticpolymer layer.

Alternatively, in accordance with a preferred embodiment of the presentinvention, the metal pigment is dispersed within the secondUV-protective transparent thermoplastic polymer layer.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the thermoplastic polymer is one of a group including:polycarbonate (PC), polyvinylchloride (PVC), polymethylmethacrylate(PMMA), polyethylenterphtalateglycol (PETG) and polystyrene (PS).

Additionally, in accordance with a preferred embodiment of the presentinvention, the sheet is one of a group of a flat sheet, a corrugatedsheet and a multi-wall sheet.

Moreover, in accordance with a preferred embodiment of the presentinvention, the sheet has an upper face and flakes of the metal pigmentare oriented coplanar to the upper face.

There is provided, in accordance with a preferred embodiment of thepresent invention, a method for production of a rigid light transmittingthermoplastic polymer sheet, the method including the steps of treatingmetal pigment flakes thereby to increase their surface energy, andfeeding a thermoplastic polymer material and the metal pigment flakesinto an extrusion line, thereby forming a melt. The method includes aswell the steps of extruding the melt through an extrusion die, andsolidifying the melt into a rigid sheet

Moreover, in accordance with a preferred embodiment of the presentinvention, the method of production includes the step of thermoformingthe rigid sheet.

Furthermore, in accordance with a preferred embodiment of the presentinvention, the step of thermoforming is performed on-line or off-line.

Additionally, in accordance with a preferred embodiment of the presentinvention, the thermoplastic polymer material is one of a groupincluding: PC, PVC, PMMA, PETG and PS.

There is provided, in accordance with a preferred embodiment of thepresent invention, a method for production of a rigid,light-transmitting thermoplastic polymer sheet, the method including thesteps of treating metal pigment flakes thereby to increase their surfaceenergy, feeding a first thermoplastic polymer material into a firstextrusion line, feeding a second thermoplastic polymer material into asecond extrusion line, and feeding the metal pigment flakes into atleast one of the extrusion lines. The method includes as well the stepsof co-extruding the first thermoplastic polymer material and the secondthermoplastic polymer material into a melt, whereby the secondthermoplastic polymer material forms a layer on the first thermoplasticpolymer material, extruding the melt through an extrusion die, andsolidifying the melt into a rigid sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with theappended drawings in which like reference numerals indicate similar orlike components. In the drawings:

FIG. 1A is a schematic illustration of a cross-section of a prior artsheet which is clear and not tinted;

FIG. 1B is a schematic illustration of a cross-section of a prior artsheet which is clear and tinted;

FIG. 1C is a schematic illustration of a cross-section of a prior artglass sheet, coated with a reflective coating and a protective layer;

FIG. 1D is a schematic illustration of a cross-section of a prior artplastic sheet, coated with a metallic surface coating and a protectivelayer;

FIG. 2 is a schematic cross-section illustration of a solar controlpolycarbonate (PC) sheet with a skin layer of UV-protective PC,according to a preferred embodiment of the present invention;

FIG. 3 is a schematic cross-section illustration of a PC sheet with askin layer of solar control, UV-protective PC, according to anotherpreferred embodiment of the present invention;

FIG. 4 is a schematic cross-section illustration of a solar control PCsheet, according to a further preferred embodiment of the presentinvention;

FIG. 5 is a block diagram illustration of a system for the production ofthe polycarbonate sheet of FIG. 2, according to a preferred embodimentof the present invention; and

FIG. 6 is a schematic flowchart of the operation of the system of FIG.5.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The solar control thermoplastic polymer sheet of the present inventionis produced by introducing a metal pigment in the form of flakes duringthe manufacture of the thermoplastic polymer sheet. The metal pigmentflakes transmit a controlled amount of light while reflecting asignificant amount and absorbing the rest. Any suitable transparentthermoplastic polymer, such as polycarbonate (PC), polyvinylchloride(PVC), polymethylmethacrylate (PMMA), polyethylenterphtalateglycol(PETG), or polystyrene (PS), can be used. The following descriptionrefers to polycarbonate (PC) for the purposes of example only and is notlimited thereto.

Reference is now made to FIG. 2, which is a schematic illustration of across-section of a PC sheet 30, according to a preferred embodiment ofthe present invention. The PC sheet 30 comprises a rigid, bulk, solarcontrol PC sheet 32 and a rigid skin layer 34 of UV-protective PC. Theaddition of the skin layer 34 of UV-protective PC makes the PC sheet 30particularly suitable for outdoor use, as is known in the art.

The skin layer 34 is applied via co-extrusion, but it will be apparentto those skilled in the art that any other suitable method for applyingthe skin layer may be utilized. In a non-limiting example, the skinlayer 34 of UV-protective PC has a thickness of 30 microns. In apreferred embodiment, a PC sheet for outdoor building is preferablycomposed of a 30-micron layer of UV-protective PC and a 1-2 mm layer ofbulk, solar control PC.

The solar control PC sheet 32 comprises polycarbonate and particles 36of metal pigment. Much of the incident radiation, shown by solid lines,is reflected off the metal pigment particles 36, while some is absorbed,and the rest, shown by dotted lines, is transmitted. In order to get anefficient effect of reflectance and transmittance, the size and shape ofthe pigment particles 36 are carefully designed and controlled, so thata minimum amount of pigment yields an optimum performance.

The optimum pigment particle 36 should be a flat and thin flake in orderto achieve maximum surface reflectance with minimum material.Essentially, the particle 36 should be a flake with a high aspect ratio(diameter to thickness), for example between approximately 10:1 and100:1. In addition, the size of the particle 36 should be less thanapproximately 50 microns in its longest dimension, since 50 microns isthe visible limit of the unaided human eye to distinguish a particle. Anapparent diameter of more than 50 microns would cause the imagetransmitted by the light to look dotted or stained.

However, the size of the particle 36 should also be significantly largerthan the wavelengths that need to be transmitted, in order for lightrays to pass efficiently without interference and in order for thereflected light to be reflected efficiently. Therefore, the size of theparticle 36 should be greater than 1-2 microns.

Finally, the flakes must be oriented parallel to the sheet surface sincethe sheet is essentially flat, and the light is incident perpendicularlyto the surface. Any particle 36 incorrectly oriented would notcontribute to the reflectance, but would rather increase the absorptionand therefore be a waste of expensive pigment.

Thus, the properties of the optimal particle 36 can be summarized asfollows:

a. a surface diameter of 5-50 microns;

b. a small a thickness as possible, preferably below 1 micron, providedthat the particle does not break during the manufacture of the sheet;

c. oriented parallel to the sheet surface.

Reference is now made to FIG. 3, which is a schematic illustration of across-section of a PC sheet 40, according to another preferredembodiment of the present invention. The PC sheet 40 comprises a rigid,bulk PC sheet 42 and a rigid skin layer 44 of solar control,UV-protective PC. Due to the skin layer 44 of UV-protective PC, thisembodiment of the present invention is particularly suitable for outdooruse.

The skin layer 44 is applied via co-extrusion, but it will be apparentto those skilled in the art that any other suitable method for applyingthe skin layer may be utilized. In a non-limiting example, the skinlayer 44 of solar control, UV-protective PC has a thickness of 30microns. In a preferred embodiment, a PC sheet for outdoor building ispreferably composed of a 30-micron layer of solar control, UV-protectivePC and a 1-2 mm layer of bulk PC.

The solar control, UV-protective PC layer 44 comprises UV-protectivepolycarbonate and particles 46 of metal pigment. Much of the incidentradiation, shown by solid lines, is reflected off the metal pigmentparticles 46, while some is absorbed, and the rest, shown by dottedlines, is transmitted. The properties of the optimal metal pigmentparticle 46 are identical to those described hereinabove with referenceto FIG. 3.

Reference is now made to FIG. 4, which is a schematic illustration of across-section of a rigid, bulk, solar control PC sheet 50, according toa further preferred embodiment of the present invention. The solarcontrol PC sheet 50 comprises polycarbonate and particles 52 of metalpigment. Most of the incident radiation, shown by solid lines, isreflected off the metal pigment particles 52, while some is absorbed,and the rest, shown by dotted lines, is transmitted. Due to the lack ofa skin layer of UV-protective PC, this embodiment of the presentinvention is particularly suitable for indoor use, when a metallic lookis desired. The properties of the optimal metal pigment particle 52 areidentical to those described hereinabove with reference to FIG. 3

The PC sheets 30 (FIG. 2), 40 (FIG. 3) and 50 (FIG. 4) are shown asbeing flat, having been extruded through a flat sheet die. It will beappreciated that any shape of sheet may be produced, depending on thedie used.

It will also be appreciated that the more the pigment is concentratednear the upper surface of the PC sheet, the better the solar properties.

Reference is now made to FIG. 5, which is a block diagram illustrationof a system suitable for the production of the polycarbonate sheet ofFIG. 2, according to a preferred embodiment of the present invention.The system comprises an extruder 60, a co-extruder 62, a flat sheetextrusion die 64, a thermoformer 66, an edge trimmer 68, a cross cutter70 and a stacker 72 The aforementioned components are well known in theart and will not be further described.

Reference is now made additionally to FIG. 6, which is a schematicflowchart of the operation of the system of FIG. 5. In operation, metalpigment flakes 74 are treated (step 100) on the outside so as toincrease their surface energy. Any suitable treatment of the metalpigment flakes, such as for example the treatments described in U.S.Pat. No. 5,773,492 to Ferguson, U.S. Pat. No. 5,558,705 to Keemer etal., and U.S. Pat. No. 4,544,600 to Kern, is acceptable. The pigmentflakes 74 and a polycarbonate (PC) material 76 are then fed (step 102)into the extruder 66, creating a pigmented PC melt. The treatment of thepigment flakes 74 allows good wetting by the PC material 76 and enhancesthe dispersiveness of the metal pigment flakes 74 in the PC material 76.In contrast, untreated metallic powders do not readily disperse inpolymer matrixes and tend to agglomerate and adversely affect mechanicalproperties of the polymer.

A special PC compound 78 with increased UV resistance properties is fed(step 104) into the co-extruder 62, creating a UV-protective PC melt.Proximate the exit of extruder 60, the UV-protective PC melt is combined(step 106) with the pigmented PC melt into a melt. This process, knownas skin layer UV co-extrusion, is well known in the art.

The melt consisting of the pigmented PC melt and the UV-protective PCmelt is forced (step 108) through the flat sheet extrusion die 64. Atthe exit of the melt from the extrusion die 64, the pigment flakes 74 inthe pigmented PC melt are oriented in the plane of the sheet, due to thehigh shear rates in the lips of the extrusion die 64. This furtheroptimizes the dispersion and effectiveness of the pigment flakes 74. Themelt is then solidified (step 110) into a flat sheet. The flat sheet maybe solid (single wall) or hollow (multi wall).

The flat sheet can be used as is or can be further thermoformed eitheron-line or off-line. On-line thermoforming alters the flat sheets intocorrugated sheets. Off-line thermoforming of more complex or small sizearticles is a preferred method for producing roof ridges, roof tiles,flashings and accessories.

If thermoforming is used, the flat sheet is passed (step 112) throughthe thermoformer 66. The corrugated (or flat) sheet is trimmed (step114) by the edge trimmer 68, cut (step 116) to its final size by thecross cutter 70 on-line and stacked (step 1 18) by the stacker 72 onpallets for shipment.

It will be appreciated that the production system of FIG. 5 and themethod of FIG. 6 can be used for the production of the polycarbonatesheet of FIG. 3, by adding the treated metal pigment flakes to theUV-protective PC compound instead of to the bulk PC material.

It will also be appreciated that the production system of FIG. 5 and themethod of FIG. 6 can be used for the production of the polycarbonatesheet of FIG. 4, by excluding the co-extrusion of the UV-protective PClayer.

Reference is now made to Table 1, which is a comparison of the opticaland solar properties of conventional clear and tinted polycarbonateroofing sheets and a PC sheet according to a preferred embodiment of thepresent invention. The first column lists the products being compared.Those sheets which are pigmented are characterized by the type ofpigment and their visible light transmission. Sheets of pigmented solarcontrol PC, in accordance with a preferred embodiment of the presentinvention, are listed in the last two rows. For each product, thefollowing optical and solar properties are given: percentage of lighttransmission (%LT), percentage of solar transmission (%ST), percentageof solar reflection (%SR), percentage of solar absorption (%SA), andshading coefficient (SC)

TABLE 1 Solar Properties of Some Common Rooflight and Skylight SheetsProduct % LT % ST % SR % SA SC Clear Polycarbonate (PC) 90 86 10 4 1.0Transparent “Bronze” Tinted PC 35% 35 42 6 52 0.64 (LT) Transparent“Bronze” Tinted PC 20% 20 28 6 66 0.52 Transparent “Solar Gray” TintedPC 35 42 6 52 0.64 35% Transparent “Solar Gray” Tinted PC 20 27 6 670.51 20% Opal (Diffused) White PC 45% 45 46 43 11 0.56 Opal (Diffused)White PC 35% 35 40 47 13 0.50 Surface Metallized Solar Control PC 35 3517 48 0.54 35% Surface Metallized Solar Control PC 20 18 28 54 0.37 20%Pigmented Solar Control PC 35% 35 32 28 40 0.49 Pigmented Solar ControlPC 20% 20 18 30 52 0.37

The lower the shading coefficient (SC), the lower the heat gain insidethe building. The sheets of pigmented solar control PC have the desiredproperties of controlled light transmission, high solar reflection, andlow shading coefficient.

PC, PVC and PETG sheets have the added benefit of being impermeable toUV light, thus further reducing the shading coefficient.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed herein above. Rather the scope of the invention is defined bythe claims that follow.

What is claimed is:
 1. A rigid light transmitting thermoplastic polymersheet having an upper face, the sheet comprising: transparentthermoplastic polymer matrix having flakes of metal pigment embeddedtherein, said flakes being substantially evenly dispersed within saidtransparent thermoplastic polymer matrix and oriented coplanar with saidupper face.
 2. A sheet according to claim 1, wherein said thermoplasticpolymer is one of a group including: polycarbonate (PC),polyvinylchloride (PVC), polymethylmethacrylate (PMMA), polysterene (PS)and polyethylenterphtalateglycol (PETG).
 3. A sheet according to claim1, wherein said sheet is one of a group comprising a flat sheet, acorrugated sheet and a multi-wall sheet.
 4. A sheet according to claim1, wherein said flakes have a diameter to thickness ratio in a range100:1 and 10:1.
 5. A sheet according to claim 1, wherein said flakeshave a surface diameter between 5 to 50 microns and a thickness lessthan 5 microns.
 6. A rigid light transmitting thermoplastic polymersheet having an upper face comprising: a first transparent thermoplasticpolymer layer; a second UV-protective transparent thermoplastic polymerlayer co-extruded with said first layer, wherein said second layer isformed on top of said first layer; and metal pigment embedded within atleast one of said first and second layers, said metal pigment beingsubstantially evenly dispersed within said at least first and secondlayer and oriented co-planar with said upper face.
 7. A sheet accordingto claim 6, wherein said metal pigment is dispersed within said firstlayer.
 8. A sheet according to claim 6, wherein metal pigment isdispersed within said second layer.
 9. A sheet according to claim 6,wherein said thermoplastic polymer sheet is one of a group including:PC, PVC, PMMA, PETG and PS.
 10. A sheet according to claim 6, whereinsaid sheet is one of a group comprising a flat sheet, a corrugated sheetand a multi-wall sheet.
 11. A sheet according to claim 6, wherein saidsheet has an upper face and flakes of said metal pigment are orientedcoplanar with said upper face.
 12. A method for production of a rigidlight transmitting thermoplastic polymer sheet having an upper face, themethod comprising the steps of: treating metal pigment flakes thereby toincrease their surface energy; feeding a transparent thermoplasticpolymer material and said metal pigment flakes into an extrusion line,thereby forming a melt; extruding said melt through an extrusion die sothat said metal pigment being embedded and substantially evenlydispersed within said melt and oriented co-planar with said upper face;and solidifying said melt into a rigid sheet.
 13. A method according toclaim 12, further comprising the step of thermoforming said rigid sheet.14. A method according to claim 13, wherein said step of thermoformingis performed on-line.
 15. A method according to claim 13, wherein saidstep of thermoforming is performed off-line.
 16. A method according toclaim 12, wherein said thermoplastic polymer material is one of a groupincluding: PC, PVC, PMMA, PETG and PS.
 17. A method for production of arigid light transmitting thermoplastic polymer sheet having an upperface, the method comprising the steps of: treating metal pigment flakesthereby to increase their surface energy; feeding a first transparentthermoplastic polymer material into a first extrusion line; feeding asecond transparent thermoplastic polymer material into a secondextrusion line; feeding said metal pigment flakes into at least one ofsaid first and second extrusion lines; co-extruding said firstthermoplastic polymer material and said second thermoplastic polymermaterial into a melt, whereby said second thermoplastic polymer materialforms a layer on said first thermoplastic polymer material; extrudingsaid melt through an extrusion die so that said metal pigment beingembedded and substantially evenly dispersed within said melt andoriented co-planar with said upper face; and solidifying said melt intoa rigid sheet.
 18. A method according to claim 17, further comprisingthe step of thermoforming said rigid sheet.
 19. A method according toclaim 18, wherein said step of thermoforming is performed on-line.
 20. Amethod according to claim 18, wherein said step of thermoforming isperformed off-line.
 21. A method according to claim 17, wherein saidfirst thermoplastic polymer material is one of a group including; PC,PVC, PMMA, PETG and PS.
 22. A method according to claim 17, wherein saidsecond thermoplastic polymer material is one of a group including: PC,PVC, PMMA, PETG and PS.